Electromagnetic actuators which essentially comprise at least one electromagnet and an armature which is connected with a setting member to be moved and which is displaceable against the force of a resetting spring by electromagnetic forces upon energization of the electromagnet are characterized by a high switching speed. These structures, however, involve the problem that as the armature approaches the pole face of the electromagnet and thus the air gap between the pole face and the armature decreases, the electromagnetic force acting on the armature progressively increases, while the counter force of the resetting spring, as a rule, only linearly increases. As a result, the armature impacts on the pole face with an increasing speed. Apart from noise generation, rebound may occur, that is, the armature first impacts on the pole face and then, at least for a short period of time, lifts off until it eventually assumes its position of rest on the pole face. This phenomenon may lead to an unsatisfactory operation of the setting member which, particularly in actuators of high switching frequency, may lead to significant disturbances.
It is therefore a desideratum that the impact velocity be in the order of magnitude of under 0.1 m/s. It is of importance in this connection that such small impact velocities should be ensured under real operational conditions including all stochastic fluctuations involved therewith. External interfering effects, for example, shocks or the like may, in the terminal approaching phase or even after engagement of the armature against the pole face, lead to a sudden drop of the armature from the pole face.